Dogs with a "food-bowl-half-empty" attitude are more likely to bark, yowl and chew when left alone than dogs with a sunnier outlook, according to a new study.

The research, which was funded by the Royal Society for the Prevention of Cruelty to Animals, may help animal shelters match dogs to appropriate homes.

Separation-related behaviors like whining, scratching, chewing and toileting indoors can prevent shelter dogs from finding good homes. In the United Kingdom, where the study was conducted, about half of family dogs act out while alone at some point in their lives, the researchers report in the Oct. 12 issue of the journal Current Biology.

Pessimistic puppies
To find out whether a tendency for separation anxiety can be predicted, study author Michael Mendl, an animal behavior and welfare researcher at the University of Bristol School of Veterinary Sciences in England, and his colleagues tested 24 shelter dogs of various breeds.

Each dog first spent 20 minutes in a room playing with a researcher. The next day, the researcher brought the same dog back to the same room, but left the animal alone for five minutes, while a camera captured the pup's reaction. The researchers then recorded how long each dog spent acting out separation anxiety.

Next, the researchers took the same dogs and trained them to associate a food bowl on one side of a room with a meal. A food bowl on the other side of the room was always empty. Once the dogs made the connection between the location and the food, the researchers mixed things up, placing an empty bowl at various ambiguous locations between the food and no-food areas.

Then they watched the dogs approach the bowls. A faster, more eager approach was taken to mean the dog expected to find food in the bowl. Researchers characterized those dogs as having an "optimistic" decision-making style.

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A good home
When the researchers compared the dogs' decision-making styles with their separation-related behaviors, they found the dogs that approached ambiguous food bowls eagerly were much more relaxed about being left alone than the "bowl-half-empty" types.

"This work and others showed that the test of separation-related behaviors is quite a good predictor of whether these dogs go on to develop the behaviors when re-homed," Mendl told LiveScience.

It's not entirely clear if the "pessimistic" dogs experience pessimism as humans do, Mendl said. For one thing, researchers tested the animals at one point in time, so they don't know if the pessimism is a stable trait in the dogs' temperaments. But given the similarities between dogs' brains and our own, it seems possible that dogs (and other mammals) might experience emotions as humans do, Mendl said.

"One can never be sure, unfortunately," he said.

"I don't think this study really gets to pessimism and optimism, but it doesn't mean that other studies couldn't," said Marc Bekoff, a professor emeritus of ecology and evolutionary biology at the University of Colorado at Boulder, who was not involved in the study. Bekoff, the author of "The Animal Manifesto: Six Reasons for Expanding Our Compassion Footprint" (New World Library, 2010), said he doesn't doubt that animals can have pessimistic or optimistic tendencies, just whether the food-bowl test can flesh those tendencies out.

Ultimately, Bekoff said, the research is important because of its practical applications in matching dogs to the homes most likely to accept them.

"I like this study, because I think it's important when people adopt dogs, rescue dogs, that they have an idea of who they're getting," Bekoff said.